The Messenger of Allah ﷺ said, "When a man stands for prayer, or when one of you prays, he should not spit in front of him, nor to his right, but to his left if that side is clear, or under his left foot, and then rub it with his foot."
قال رسول الله ﷺ: إذا قام الرجل إلى الصلاة، أو إذا صلى أحدكم فلا يبزق أمامه، ولا عن يمينه ولكن عن تلقاء يساره إن كان فارغا، أو تحت قدمه اليسرى، ثم ليقل به.
Reported by Abu Dawud (478), and this is his wording, Tirmidhi (571), Nasai (726), and Ibn Majah (1/326) (1021), all of them through the route of Mansur, from Rabi bin Harash, from Tariq bin Abdullah, who then related the hadith. The wording of Nasai is, "If he had time, otherwise like this," and he spat under his foot and rubbed it. Tirmidhi said, hasan sahih. He said, I heard Jarud say, I heard Waki say, Rabi bin Harash never told a single lie since embracing Islam. Abdul-Rahman bin Mahdi said, the most reliable of the people of Kufa was Mansur bin Mutamir.I say, Rabi bin Harash, with the ra and ha vowelled with a kasra, Abu Maryam Absi Kufi. Ajli said, he was a trustworthy successor, among the best of people. Ibn Saad said, he was trustworthy and had sound hadiths. He died in the year 100, or it is said after that. Ibn Khuzayma (877, 876) and Hakim (1/256) graded it sahih.